Electronic still camera and image processing method

ABSTRACT

Provide an electronic still camera using a color filter array (CFA) and a single CCD making it possible to simultaneously execute the processing for color signal interpolation and the processing for resizing. In the electronic still camera according to the present invention, an R signal, a G signal, and a B signal are output from each pixel of an image sensor  12  having a CFA. A processor  16  simultaneously executes processing for interpolation and processing for resizing by computing (R, G, B) values at a given pixel position according to the color signals. Low frequency components R low , G low , B low  of the color signal at the given pixel position are computed from signals from adjoining pixels, and the high frequency component S high  is computed from a brightness value Y. The image data interpolated and changed to a desired size is stored in a memory  18,  or is output via an interface I/F  20  to an external device such as a computer or a printer.

FIELD OF THE INVENTION

[0001] The present invention relates to an electronic still camera and to an image processing method, and more specifically to processing for interpolation and processing for changing the size (resizing) of an image.

BACKGROUND OF THE INVENTION

[0002] Color filter arrays (CFA) and single CCD arrays (or CMOS arrays) are used in electronic still cameras (including digital cameras). With a combination of a CFA and a single CCD array, an R signal, a G signal, or a B signal are output from each pixel of the CCD array, and color image data is obtained from these signals. Because the signal from each pixel is a monochromatic signal, it is necessary to interpolate remaining color signals from signals from other pixels. For instance, with a Bayer type CFA, G pixels and B pixels are arrayed alternately in one line, and G pixels and R pixels are arrayed alternately in the next line. Because the R pixels cannot generate signals for G and B values required for color image data, it is necessary to interpolate the G value and B value at the R pixel position with signals from G pixel and B pixels near the R pixel. This is also applicable to other pixels, and it is necessary to interpolate R and B values at a G pixel and to interpolate R and G values at a B pixel. Further, when a color image consisting of a number of pixels more or less than those of a CCD array is to be output, it is necessary to resize the image data having been subjected to interpolation (for improving the resolution). Generally a bi-linear interpolation or a bi-cubic interpolation is employed for resizing.

SUMMARY OF THE INVENTION

[0003] In the conventional technology as described above, the processing is very complicated because it is necessary to execute CFA interpolation and resizing separately. Further, it is necessary to perform processing for changing the resolution, namely for enlarging or reducing a size of an image according to the pixel data obtained through the interpolation processing, and especially when processing for enlarging an image is performed, sharpness of the image may be lost.

[0004] The present invention was made in light of the circumstances described above, and it is an object of the present invention to provide an electronic still camera and an image processing method which simplify the required processing by making it possible to simultaneously execute the processing for interpolation and the processing for resizing (or for improving the resolution) and which can also prevent degradation of image quality.

[0005] To achieve the object described above, an electronic still camera according to the present invention has an image pickup means having a color filter array and outputting a color signal for each pixel in a prespecified pixel array, an A/D conversion means for converting a signal from said image pickup element to a digital one, and a processing means for generating an image having a desired size by interpolating the color signal at a given pixel position according to the color signal for each pixel.

[0006] Herein, the processing means preferably separates a low frequency component of a color signal to be interpolated from a high frequency component thereof, interpolates the low frequency component according to color signals from a plurality of pixels for the same color surrounding and adjoining a pixel position to be interpolated, and also interpolates the high frequency component according to a brightness value at the pixel position to be interpolated as well as to those at a plurality of pixel positions surrounding and adjoining the pixel position to be interpolated.

[0007] The processing means preferably further computes an edge component of the image according to the high frequency component.

[0008] In the camera according to the present invention, the image pickup means outputs an R signal, a G signal, or a B signal for each pixel, while the processing means interpolates a low frequency component of the R signal according to signals from a plurality of R signal pixels surrounding and adjoining a pixel position to be interpolated, interpolates a low frequency component of the B signal according to signals from a plurality of B signal pixels surrounding and adjoining the pixel position to be interpolated, and further interpolates a low frequency component of the G signal according to signals from a plurality of G signal pixels surrounding and adjoining the pixel position to be interpolated.

[0009] The color filter array may be, for example, a Bayer filter array, and the processing means preferably interpolates a low frequency component of the R signal according to signals from four R signal pixels surrounding and adjoining a pixel position to be interpolated, interpolates a low frequency component of the B signal according to signals from four B signal pixels surrounding and adjoining the pixel position to the interpolated, and further interpolates a low frequency component of the G signal by generating four virtual pixels from G signal pixels surrounding and adjoining the pixel position to be interpolated and according to G signal values for the four virtual G signal pixels. Further, the processing means computes a brightness value at an intermediate pixel position among those in the prespecified pixel array, computes brightness values at four peripheral pixel positions forming a square having diagonal lines, at a cross point of which is located said pixel position to be interpolated from the brightness value at the intermediate pixel position, and further interpolates high frequency components of the R signal, G signal, and B signal according to the brightness value at the pixel position to be interpolated and those at the peripheral pixel positions.

[0010] Further, the present invention provides a method of processing image data obtained with a color filter array and an image pickup element. This method comprises the step of generating new image data by simultaneously executing, according to a color signal for each pixel of said image pickup element, the processing for interpolating said color signal at other pixel position and the processing for changing a size of said image.

[0011] This method preferably further comprises the step of generating new image data by simultaneously executing, according to a color signal for each pixel of said image pickup element, the processing for interpolating said color signal at other pixel position and the processing for changing a size of said image.

[0012] As described above, with the present invention, by simultaneously executing processing for interpolation and processing for resizing (for improving the resolution), a complicated processing for resizing after interpolation is not required, and degradation of image quality can be prevented. The processing for interpolation according to the present invention can be executed by computing a color signal at a pixel position required for resizing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIG. 1 is a schematic block diagram showing an electronic still camera according to an embodiment of the present invention;

[0014]FIG. 2 is a functional block diagram showing a processor according to the embodiment;

[0015]FIG. 3 is a functional block diagram showing a processor based on a conventional technology;

[0016]FIG. 4 is a graph showing the relation between K_(sharp) and K_(smooth) in the embodiment;

[0017]FIG. 5 is a flowchart showing the general processing flow in the embodiment;

[0018]FIG. 6 is an explanatory view showing the processing for computing a brightness value Y;

[0019]FIG. 7 is an explanatory view showing the processing for computing R_(low) and B_(low) in the embodiment;

[0020]FIG. 8 is an explanatory view showing the processing for computing G_(low) in the embodiment; and

[0021]FIG. 9 is an explanatory view showing the processing for computing S_(high) in the embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0022] An embodiment of the present invention is described below with reference to the related drawings.

[0023]FIG. 1 is a schematic block diagram showing an example electronic still camera 1 according to an embodiment of the present invention. An electronic still camera 1 comprises an optical system including a lens 10, an image sensor 12 such as a CCD array or a CMOS array, an A/D converter 14, a processor 16, a memory 18, and an interface I/F 20.

[0024] The image sensor 12 includes the Bayer type CFA, and outputs any of an R signal, a G signal, and a B signal from each pixel thereof. In the Bayer CFA, G pixels and B pixels are arrayed alternately in alternating lines in the two-dimensional array, and G pixels and R pixels are arrayed alternately in the other lines. A color signal output from each pixel of the image sensor 12 is converted to a digital signal in the A/D converter 14, and is fed to the processor 16.

[0025] The processor 16 executes a processing for interpolation and a processing for resizing each described below, and stores image data obtained through this processing in the memory 18. Further, the processor 16 reads out the image data stored in the memory 18, and outputs the read-out image data via the interface I/F 20 to an external device such as, for example, a computer system or a printer.

[0026] In an electronic still camera based on the conventional technology, when a size of an image obtained with the image sensor 12 is enlarged or reduced, the processor 16 processes the image data obtained by interpolating color signals to the processing for improving the resolution so that the resolution corresponding to the specified size can be obtained, stores the image data in the memory 18 or outputs the image data via the interface I/F 20. On the other hand, in this embodiment of the present invention, the processor 16 simultaneously executes the processing for interpolation and the processing for resizing, in other words simultaneously changes the resolution of the image during the processing for interpolation, and generates image data having a desired size with a set of (R, G, B values).

[0027]FIG. 2 is a functional block diagram showing the processing 16 in FIG. 1. The processor 16 has a CFA interpolation section, a color correction section, and a JPEG compression section each as a functional block. The CFA interpolation section generates a set of (R, G, B values) at a given pixel position from an R signal, a G signal, and a B signal from each pixel outputted from the image sensor 12. By generating color signals at the given pixel position, the processor 16 simultaneously executes the processing for interpolation and the processing for resizing (the processing for improving the resolution). By generating an R value, a G value, and a B value at a given pixel position (including an intermediate pixel position among those in a prespecified array) in the prespecified pixel array of the image sensor 12, the processing for interpolation is executed to generate image data with a desired resolution. For example, to improve the resolution to a two times higher level, it is only necessary to generate one other set of (R, G, B values) at an intermediate pixel position in the original CFA pixel array and add the set to the original set of (R, G, B values).

[0028] The image data having been subjected to interpolation and resizing is provided to the color correction section, where color correction of parameters such as white balance is performed and the image data is then compressed in the JPEG compression section.

[0029]FIG. 3 is a functional block diagram showing the processor 16 in the electronic still camera 1 based on the conventional technology as a comparative example. As described above, in an electronic still camera based on the conventional technology, the processing for enlarging or reducing a size of an image is performed after CFA interpolation, and the processor 16 is functionally divided to the interpolation section and the enlargement/reduction section as shown in the figure. Superiority over the conventional technology of the present invention as embodied in the above description can readily be understood by comparing FIGS. 2 and 3.

[0030] The processing for interpolation and the processing for resizing as performed in this embodiment are described in detail below.

[0031] First, in this embodiment, a color signal is divided to a low frequency component and a high frequency component. Specifically, the processing above can be expressed by the following equations:

R=R _(low) +S _(high)

G=G _(low) +S _(high)

B=B _(low) +S _(high)  (1)

[0032] Of the signal components above, the low frequency components R_(low), G_(low), and B_(low) are computed by linearly interpolating color signals from a plurality of pixels adjoining the pixel position to be interpolated.

[0033] On the other hand, the high frequency component S_(high) is divided to a sharpness component S_(sharp) and a noise smoothing element S_(smooth) . Specifically, the following equation is applicable:

S_(high) =K _(sharp) ×S _(sharp) −K _(smooth) ×S _(smooth)  (2)

[0034] Here, S_(sharp) and S_(smooth) are calculated according to a virtual brightness signal Y computed from a color signal from the image sensor 12. K_(sharp) and K_(smooth) are parameters used for controlling amplitudes of S_(sharp) and S_(smooth), and are derived from a secondary differential value Diff of the brightness value Y signal.

Diff=|S _(sharp) |+|S _(smooth)|

K _(sharp=() Diff/Thr)×K

K _(smooth) =K−K _(sharp)  (3)

[0035]FIG. 4 shows the relation between K_(sharp) and K_(smooth). K and Thr are parameters which are set to respective prespecified values, and, when the value Diff is not more than the threshold value Thr, K_(sharp) and K_(smooth) are complementary to each other, and as the differential value Diff increases (the image changes rapidly), K_(smooth) decreases while K_(sharp) increases. When the value Diff is greater than the threshold value Thr, K_(sharp) increases to the maximum value K and K_(smooth) is reduced to zero.

[0036] The processor 16 executes the processing for interpolation (interpolation accompanying the process for resizing) by computing a low frequency component and a high frequency component at a given pixel position to compute a set of (R, G, B values).

[0037]FIG. 5 is a flowchart showing the general sequence of the processing executed by the processor 16. First, the processor 16 computes a brightness value Y according to color signals outputted from pixels of the image sensor 12 (S101). More specifically, the processor 16 computes a brightness value Y at an intermediate pixel position among the original CFA pixel positions according to signals from the adjoining R pixels, G pixels, and B pixels. Then the processor 16 computes a low frequency component R_(low) for R at a pixel position to be interpolated (S102), and further computes a low frequency component Blow for B at the pixel position to be interpolated (S103). Computation for R_(low) and B_(low) is performed using an R value for an R pixel and a B value for a B pixel surrounding and adjoining the pixel position to be interpolated. The pixel position to be interpolated is decided according to the size desired for an image to be generated.

[0038] After the respective low frequency components R_(low), B_(low) for R and B are calculated, a low frequency component G_(low) for G is calculated. The low frequency component G_(low) for G is calculated by first computing a virtual G pixel and then using this virtual G pixel (S104, S105). The virtual G pixel is calculated because the G pixels are arrayed linearly (on a diagonal line) in a Bayer CFA.

[0039] After the low frequency components R_(low), G_(low), and B_(low) at the position to be interpolated, and high frequency components S_(high) for each color are calculated (S106), finally the (R, G, B) values at the pixel position to be interpolated are determined (S107).

[0040] Each processing step is described in more detail below.

[0041] Computing the Brightness Value Y (S101)

[0042]FIG. 6 shows the processing for computing the brightness value Y in step S101. In this figure, R indicates an R pixel, G indicates a G pixel, and B indicates a B pixel. In the Bayer CFA, G pixels and B pixels are arrayed alternately, such as for example, G00, B01, G02, B03, G04, in a line as shown in the figure. G pixels are arrayed linearly along diagonal lines. A brightness value Y for a central pixel position among the CFA pixels is computed. In FIG. 6, Y00 is shown as a central position among G11, R12, B21, G22; Y01 is shown as a central position among R12, G13, G22, B23; Y10 is shown as a central position among B21, G22, G31, R32; and Y11 is shown as a central position among G22, B23, R32, and G33. The brightness value Y at Y00 is computed from a total of 10 adjoining pixels, namely G11, G22, R12, B21, R10, B01, R32, B23, R30, and B03. More specifically, Y00 is computed through the following formula:

Y00=ratio G×(G11+G22)/2+ratio C×{9×(R12+B21)+3×(R10+B01)+d×(R32+B23)+(R30+B03)}/32  (4)

[0043] It should be noted that the R component and B component in the second term is the right side are found as described below. When a value of A positioned at Y00 is RY00, the following equation will hold true:

[0044]RY00=¾×(¾×R12+¼×R10)+¼×(¾×R32+¼×R30)=(9×R12+3×R12+3×R32+1×R30)/16

[0045] Similarly, when a value of B positioned at Y00 is BY00, the following equation will hold true:

BY00=(9×B21+3×B23+3×B01+1×B03)

[0046] The equation above can therefore be obtained from the equation of Y00=ratio G ×(G11+G22)+ratio C×(RY00+BY00)/2

[0047] Here, the ratio G and ratio C indicates a weight of the G signal and weights of the R signal and B signal each at position Y00 respectively, and known weights of the color signals for the brightness are used. The G component in the first term in the right side is an intermediate value between pixels G11 and G22 adjoining each other, and the R component and B component in the second term in the right side are calculated by bi-linear interpolation.

[0048] Similarly Y01, Y10, and Y11 are calculated through the following equation:

Y01=ratio G×(G13+G22)/2+ratio C×{9×(R12+B23)+3×(R14+B03)+3×(R32+B219+(R34+B01))/32  (5)

Y10=ratio G×(G22+G31)/2+ratio C×{9×(R32+B21)+3×(R12+B23)+3×(R30+B41)+(R10+B43)}/32  (6)

Y11=ratio G×(G22+G33)/2+ratio C×{9×(R32+B23)+3×(R12+B21)+3×(R34+B43)+(R14+B41)}/32  (7)

[0049] Through the equations described above, the brightness value Y at a central pixel position among those in the CFA is computed. This brightness value Y is used for computing the high frequency component S_(high) at a given pixel position. More specifically, the brightness value Y is used for computing S_(sharp) and S_(smooth) of the high frequency component S_(high).

[0050] <Computing a Low Frequency Component of R and a Low Frequency Component of B (Steps S102 and S103)>

[0051]FIG. 7 shows the steps S102 and S103 of computing R_(low) and B_(low). It is assumed herein that the R_(low) and B_(low) of the pixel X at the position P is computed. It is also assumed that the pixel X is separated from the reference position by a distance h in the horizontal direction and by a distance v in the vertical direction. R_(low) at the pixel X is then computed from R32, R34, R52, R54 which are four pixels for the same color adjoining the pixel X. In this case, the following equation can be applied: $\begin{matrix} {\left. {{\left. {R_{low} = \left\lbrack {{\left( {2 - v} \right)x\left\{ {{\left( {1 + h} \right) \times R\quad 34} + {\left( {1 - h} \right)x\quad R\quad 32}} \right\}} + {v\quad x\left\{ {{\left( {1 + h} \right)xR\quad 54} + {\left( {1 - h} \right) \times \quad R\quad 52}} \right\}}} \right\rbrack} \right\rbrack/4} = \left\{ {{\left( {2 - v} \right) \times \left( {1 + h} \right) \times \quad R\quad 34} + {\left( {2 - v} \right) \times \left( {1 - h} \right) \times R\quad 32} + {V \times \left( {1 + h} \right) \times \quad R\quad 54} + {v \times \left( {1 - h} \right) \times R\quad 52}} \right\}} \right\}/4} & (8) \end{matrix}$

[0052] On the other hand, B_(low) is computed from B23, B25, B43, B45 which are pixels for the same color adjoining the pixel X.

[0053] In this case, the following equation can be used: $\begin{matrix} {\left. {B_{low} = {{\left\lbrack {{\left( {1 + v} \right) \times \left\{ {{\left( {2 - h} \right) \times B\quad 43} + {h \times B\quad 45}} \right)} + {\left( {1 - v} \right) \times \left\{ {{\left( {2 - h} \right) \times B\quad 23} + {h \times B\quad 25}} \right\}}} \right\rbrack/4} = {{\left\{ {1 + v} \right) \times \left( {2 - h} \right) \times B\quad 43} + {\left( {1 + v} \right) \times h \times B\quad 45} + {\left( {1 - v} \right) \times \left( {2 - h} \right) \times B\quad 23} + {\left( {1 - v} \right) \times h \times B\quad 25}}}} \right\}/4} & (9) \end{matrix}$

[0054] <Computing a Low Frequency Component of G (S104 and S105)>

[0055] <Computing a Virtual G Pixel (S104)>

[0056]FIG. 8 illustrates the computations at step S104 related the virtual G pixel. As described above, the G_(low) of the pixel X at the position P is computed from the virtual G pixel. The virtual G pixel G′ is at the central position among the CFA pixels as shown in FIG. 8, and four virtual G′ pixels surround the pixel X. The G′11 is at a central position among G22, R23, R32, G33; G′12 is at a central position among R23, G24, G33, R34; G′21 is at a central position among R32, G33, G42, B43; and G′22 is at a central position among G33, R34, B43, G44. These virtual G pixels are calculated by means of linear approximation using the equations below:

G′11=(G22+G33)/2  (10)

G′12=(G24+G33)/2  (11)

G′21=(G33+G42)/2  (12)

G′22=(G33+G44)/2  (13)

[0057] <Computing G_(low) Using the Virtual G Pixels (S105)>

[0058] After the virtual G pixels G′ are found as described above, the low frequency component G_(low) of G at the pixel X is found using the values for the four virtual pixels G′. Namely, the following processing is executed:

G _(low)={(½−v)×(½−h)×G′11+(½−v)×(½+h)×G′12+(½+v)×(½−h)×G′21+(½+v)×(½+h)×G′22}}/4  (14)

[0059] <Computing the High Frequency Component S_(high) (S106)>

[0060]FIG. 9 shows the processing for computing a high frequency component S_(high) of a color signal in the step S106. The S_(high) at the pixel X is calculated according to brightness values Y at four pixel positions forming a square, at a cross point of diagonal lines of which is positioned the pixel X. FIG. 9 shows the pixels each as T′, and the pixel X is positioned at a cross point between the two diagonal lines among pixel positions Y′00, Y′02, Y′21, and Y′22. Y′00, Y′02, Y′21, and Y′22 are calculated from the brightness values found at step S101, namely from brightness values at a position central to four CFA pixel positions. More specifically, Y′00 is computed from a brightness value at a position central to Y00, Y01, Y10, Y11; Y′02 is computed from a brightness value at a position central to Y02, Y03, Y12, Y13; Y′20 is computed from a brightness value at a position central to Y20, Y21, Y30, Y31; and Y′22 is computed from a brightness value at a position central to Y22, Y23, Y32, Y33.

[0061] These operations are executed using the following equations, respectively:

Y′00={(½−V)×(½−h)×Y00+(½−v)×(½+h)× Y 01 +(½+v)×(½−h)×Y10+(½+v)×(½+h)×Y11 }/2  (15)

Y′02={(½−v)×(½−h)×Y02+(½−v)×(½+h)Y03+(½+v)×(½−h)×Y12+(½+v)×(½+h)×Y13 }/2  (16)

Y′20={(½−v)×(½−h)Y20+(½−v)−(½+h)×Y21 +(½+v)×(½−h)×Y30+(½+v)×(½+h)×Y31 }}/2  (17)

Y′22={(½−v)×(½−h)×Y22+(½−v)×(½+h)×Y23+(½+v)×(½−h)×Y32+(½+v)×(½+h)×Y33 }}/2  (18)

[0062] S_(sharp) and S_(smooth) each representing the high frequency component S_(high) at the pixel X are calculated from a brightness value Yx at the pixel X and from the brightness values Y′ at pixels adjoining the pixel X through the following equations:

S _(sharp)=2×Yx−Y′00−Y′22  (19)

S _(smooth)=2×Yx−Y′02−Y′20  (20)

[0063] Herein the brightness Yx at the pixel X is calculated from the brightness values at the pixels Y11, Y12, Y21, Y22 surrounding and adjoining the pixel X using the following equation:

Yx={(½−v)×(½−h)×Y11+(½−v)×(½+h)×Y12+(½+v)×(½−h)×Y21+(½+v)×(½+h)×Y22 }/2  (21)

[0064] The low frequency component and the high frequency component of the pixel X at the position P are calculated, and the R, G, B values at the pixel X (Rx, Gx, Bx) are obtained through the following equations:

Rx=R _(low) +S _(high)

Gx=G _(low) +S _(high)

Bx=B _(low) +S _(high)  (22)

[0065] The processing in this embodiment is as described above, and in this embodiment the S_(sharp) and S_(smooth) are found for computing the high frequency component S_(high) of a color signal, and these values can be used to emphasize an edge of an image. The processing for emphasizing an edge of an image is described below.

[0066] <Emphasis of an Image Edge>

[0067] The signal S′ having been subjected to the processing for edge emphasis can be expressed by the following equation in the unsharp masking method:

S′=S+wx(S−S.f)  (23)

[0068] Here, S is the original signal, while S.f represents a signal which has passed through a low-pass filter and w indicates a relative weight. The signal S′ having been subjected to edge emphasis can be obtained by adding a signal obtained by subtracting the signal smoothed in the low-pass filter from the original signal to the original signal S with a specific weight. In this embodiment, the signal S is divided to a low frequency component S_(low) and a high frequency component S_(high), wherein the high frequency component S_(high) comprises S_(sharp) and S_(smooth). Therefore, the following equation is applicable:

S=S _(low) +S _(high) =S _(low) +K _(sharp) ×S _(sharp) −K _(smooth) ×S _(smooth)  (24)

[0069] Assuming that the low-pass filter f is for S_(smooth), the signal S″ after passage through the low-pass filter can be obtained through the following equation:

S″=S _(low) −K×S _(smooth)  (25)

[0070] Therefore the signal S′ having been subjected to the processing for edge emphasis can be expressed by the following equation: $\begin{matrix} \begin{matrix} {S^{\prime} = {S + {w \times \left( {S - S^{''}} \right)}}} \\ {= {S + {W \times \left( {{K_{sharp} \times S_{sharp}} - {K_{smooth} \times S_{smooth}} + {K \times S_{smooth}}} \right)}}} \\ {= {S + {w \times K_{sharp} \times \left( {S_{sharp} + S_{smooth}} \right)}}} \end{matrix} & (26) \end{matrix}$

[0071] It should be noted that the relation K_(smooth)=K−K_(sharp) is used in the equation above.

[0072] Because S_(sharp) and S_(smooth) are obtained during the processing for computing S_(high), the edge emphasis signal S′ can also be computed using these signals. Thus, in this embodiment, the processing for interpolation and the processing for resizing can be executed simultaneously, and the processing for edge emphasis can also be performed simultaneously.

[0073] As described above, with the present invention, by simultaneously executing the processing for interpolation and the processing for resizing, it is possible to simplify the processing sequence by simultaneously executing the processing for interpolation and the processing for resizing. Degradation of image quality is also thereby prevented.

[0074] PARTS LIST

[0075] 1 still camera

[0076] 10 lens

[0077] 12 image sensor

[0078] 14 A/D converter

[0079] 16 processor

[0080] 18 memory

[0081] 20 interface 

What is claimed is:
 1. An electronic still camera comprising: (a) an image pickup means having a color filter array and capable of outputting a color signal for each pixel in a prespecified pixel array; (b) an A/D conversion means for converting a signal from said image pickup element to a digital one; and (c) a processing means for generating an image having a desired size by interpolating the color signal at a given pixel position according to the color signal for each pixel.
 2. The electronic still camera according to claim 1, wherein said processing means: separates a low frequency component of the color signal to be interpolated from a high frequency component thereof; interpolates said low frequency component according to signals from a plurality of same color pixels surrounding and adjoining the pixel position to be interpolated; and interpolates said high frequency component according to a brightness value at a pixel position to be interpolated as well as to brightness values at a plurality of pixel positions surrounding and adjoining the pixel position to be interpolated.
 3. The electronic still camera according to claim 2, wherein said processing means further computes an edge component of said image according to said high frequency component.
 4. The electronic still camera according to claim 2, wherein said image pickup means outputs a R signal, a G signal, and a B signal for each pixel, while said processing means: interpolates the low frequency component of said R signal according to signals from R signal pixels surrounding and adjoining the pixel position to be interpolated; interpolates the low frequency component of said B signal according to signals from B signal pixels surrounding and adjoining the pixel position to be interpolated; and interpolates the low frequency component of said G signal according to signals from G signal pixels surrounding and adjoining the pixel position to be interpolated.
 5. The electronic still camera according to claim 4, wherein said color filter array is a Bayer filter array, and said processing means interpolates the low frequency component of said R signal according to signals from four R signal pixels surrounding and adjoining the pixel position to be interpolated; interpolates the low frequency component of said B signal according to four B signal pixels surrounding and adjoining the pixel position to be interpolated; and interpolates the low frequency component of said G signal by generating four virtual G signal pixels from G signal pixels surrounding and adjoining the pixel position to be interpolated and according to G signal values for said four virtual G signal pixels.
 6. The electronic still camera according to claim 5, wherein said processing means: computes a brightness value at an intermediate pixel position among those in said prespecified pixel array; computes brightness values at four peripheral pixel positions forming a square having diagonal lines, at a cross point of which is located said pixel position to be interpolated from the brightness value at the intermediate position; and interpolates high frequency components of said R signal, G signal, and B signal according to the brightness value at the pixel position to be interpolated and those at said peripheral pixel positions.
 7. A method of processing image data obtained with a color filter array and an image pickup element comprising the step of: generating new image data by simultaneously executing, according to a color signal for each pixel of said image pickup element, processing for interpolating said color signal at other pixel position and the processing for changing a size of said image.
 8. The image processing method according to claim 7 further comprising the steps of: generating said new image data by computing a low frequency component of a color signal at a pixel position required for obtaining a desired image size according to a color signal from each pixel of said image pickup element, computing a high frequency component of the color signal at a pixel position required for obtaining a desired image size according to a brightness signal obtained from the color signal from each pixel of said image pickup element, and adding said low frequency component to said high frequency component. 